I am only active in SO and Code Review, and I find that Code Review answers can take a bit of time, especially when fiddling around with a Plunker or JSFiddle sample or finding some reference as to why one approach is generally accepted to be better than another approach.
Right now, I actually keep a sticky open on my desktop with my review and copy/paste when it is ready. I would love Stack Exchange (or just Code Review) to have a '(auto) Save as Draft' feature so that I don't need the sticky anymore.
Your thoughts?
Edit : Apparently this already works, to be tested.